Field of the Invention
The present disclosure relates to a light-shielding paint, a light-shielding paint set, an optical element that are used for optical apparatuses, such as cameras, binoculars, and microscopes, and to a method for manufacturing the optical element.
Description of the Related Art
A light-shielding film used in an optical element is a coating film formed on, typically, a surface of a glass member. Although the optical element may be a lens, a prism or any other optical glass, a light-shielding film of a lens will be described below by way of example.
As shown in FIG. 4, a light-shielding film 1 of an optical element is formed on a periphery of a lens 2. If light impinges only on the lens 2 as incident light 3 does, the light passes through the lens as transmission light 4. On the other hand, if light obliquely enters the lens 2 as incident light 5 does, the light impinges on the light-shielding film 1. At this time, if the light-shielding film is not formed (like the lower side of the lens shown in FIG. 4), light 5 incident on the periphery of the lens 2 reflects internally and goes out of the lens 2 as internally reflected light 6 that is not involved in forming an image. This light causes flaring or ghosts, thus degrading image quality. A light-shielding film 1 formed as on the upper side of the lens shown in FIG. 4 can reduce the internal reflection of obliquely incident light 5. Accordingly, internally reflected light 6 adversely affecting the image is reduced, and flaring and ghosts are prevented.
As optical apparatuses are being downsized and required to have higher performance, materials having higher refractive indices are coming to be used for the optical elements of optical systems. For example, glass materials having a refractive index of 1.80 or more or more than 2.00 are used.
In order to reduce internal reflection of light in an optical element having a high refractive index, the refractive index of the light-shielding film is increased. Japanese Patent Laid-Open No. 2011-186437 discloses a method for controlling the refractive index of a light-shielding film by adding a material having a high refractive index to the light-shielding film.
This patent document also discloses a light-shielding film for an optical element. This light-shielding film contains inorganic non-black particles for increasing refractive index and a dye for absorbing light, so that internal reflection is reduced.
Unfortunately, the light-shielding film of this patent document has a uniform composition. If this light-shielding film is formed on a glass member, the refractive index of the entire light-shielding film must be close to the refractive index of the glass member in order to reduce internal reflection. For forming a light-shielding film on a glass member having a high refractive index, a large amount of inorganic particles having a high refractive index is added to the light-shielding film. If a large amount of inorganic particles is added to the light-shielding film, the inorganic particles form an aggregate that is likely to scatter light, thus degrading optical properties of the light-shielding film. In addition, since the resin content is relatively reduced, weather resistance can be reduced.